Yeah, I found the powders dissolved into the varnish if applied over them. If you wait for the varnish to go tacky and then apply the powders they stick to the varnish rather then dissolving.
I know people use turps to fix weathering. Does this dissolve the powder (wet look) or does it stay powdery?

Turps work fine. Makes the powder flow slightly so that the wearhering looks more natural. However, it does zilch for sealing. I am getting lazy though so I would probably not do turp on 6 mm.

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Nitpicks Knapsack (Scratchbuilding and 3D designing and printing and painting)